Emulsions are mixtures which are prepared from two mutually insoluble components. It is possible to generate mixtures of homogenous macroscopic appearance from these components through proper selection and manipulation of mixing conditions. The most common type of emulsions are those in which an aqueous component and a lipophilic component are employed and which in the art are frequently referred to as oil-in-water and water-in-oil emulsions. In oil-in-water emulsions the lipophilic phase is dispersed in the aqueous phase, while in water-in-oil emulsions the aqueous phase is dispersed in the lipophilic phase. Commonly known domestic examples of emulsion-based formulations include mayonnaise, margarine, ice cream, cosmetics and paint. Emulsion systems are also extensively applied in industries such as the pharmaceutical and the agrochemical industries, where it is often desirable to formulate active ingredients in emulsions.
Generally emulsions are prepared in the presence of a multiplicity of other substances in order to achieve a desirable balance of emulsification, viscosity, stability and appearance. For example, the formulation of emulsions usually requires at least one, and frequently a combination of several, emulsifying agents. These agents facilitate the dispersal of one immiscable phase into the other and assist in stabilizing the emulsion. Emulsifiers comprise a wide variety of synthetic and natural components. For example, monoglycerides and chemical derivatives thereof, are widely used as emulsifiers in food applications such as margarines and baked products. An example of a natural emulsifier is lecithin, a phospholipid present in egg yolk, which is commonly used in the preparation of mayonnaise. It is also possible to entrap active ingredients in emulsions. This is especially desirable in compositions comprising active agents which are difficult to dissolve in aqueous solutions, such as certain vitamins and nucleotides. Active ingredients are also frequently formulated as emulsions in order to enhance their stability. One example of an emulsion system comprising a pharmaceutical agent is documented in U.S. Pat. No. 5,602,183 which discloses a wound healing composition containing an anti-inflammatory agent. The foregoing exemplifies only a few of the myriad of components which are included in formulations of emulsions known in the art. A comprehensive overview of emulsifying agents and their applications may be found in Becher, P. Encyclopedia of Emulsion Technology, Dekker Ed., 1983.
In the seeds of oilseed crops, which include economically important crops, such as soybean, rapeseed, sunflower and palm, the water insoluble oil fraction is stored in discrete subcellular structures variously known in the art as oil bodies, oleosomes, lipid bodies or spherosomes (Huang 1992, Ann. Rev. Plant Mol. Biol. 43: 177-200). Besides a mixture of oils (triacylglycerides), which chemically are defined as glycerol esters of fatty acids, oil bodies comprise phospholipids and a number of associated proteins, collectively termed oil body proteins. From a structural point of view, oil bodies are considered to be a triacylglyceride matrix encapsulated by a monolayer of phospholipids in which oil body proteins are embedded (Huang, 1992, Ann. Rev. Plant Mol. Biol. 43: 177-200). The seed oil present in the oil body fraction of plant species is a mixture of various triacylglycerides, of which the exact composition depends on the plant species from which the oil is derived. It has become possible through a combination of classical breeding and genetic engineering techniques, to manipulate the oil profile of seeds and expand on the naturally available repertoire of plant oil compositions. For an overview of the ongoing efforts in his area, see Designer Oil Crops/Breeding, Processing and Biotechnology, D. J. Murphy Ed., 1994, VCH Verlagsgesellschaft, Weinheim, Germany.
Plant seed oils are used in a variety of industrial applications, notably in the food, detergent and cosmetics industries. In order to obtain the plant oils used in these applications, seeds are crushed or pressed and subsequently refined using processes such as organic extraction, degumming, neutralization, bleaching and filtering. Aqueous extraction of plant oil seeds has also been documented (for example, Embong and Jelen, 1977, Can. Inst. Food Sci. Technol. J. 10: 239-243). Since the objective of the processes taught by the prior art is to obtain pure oil, oil bodies in the course of these production processes lose their structural integrity. Thus, the prior art emulsions formulated from plant oils do not generally comprise intact oil bodies.
Although there are many applications where mineral oil based products dominate the market, in other applications, oils derived from plant sources and fossil sources are in direct competition. Lauric oils, for example, which are widely used in the manufacture of detergents, are obtained from mineral oil as well as from coconut oil and more recently from genetically engineered rapeseed (Knauf, V. C., 1994, Fat. Sci. Techn. 96: 408). However, there is currently an increasing demand for biodegradable sources of raw materials. The plant oil body based emulsions of the present invention offer an advantage over similar mineral oil based formulations, in that the oil fraction is derived from a renewable and environmentally friendly source.
U.S. Pat. Nos. 5,683,710 and 5,613,583 disclose emulsions comprising lipid vesicles from oleaginous plants. The emulsions disclosed in these patents are prepared from relatively crude seed extracts and comprise numerous seed components including glycosylated and non-glycosylated proteins. It is a disadvantage of the emulsions to which these patents relate that they comprise contaminating seed components imparting a variety of undesirable properties, which may include allergenicity and undesirable odour, flavour, colour and organoleptic characteristics, to the emulsions. Due to the presence of seed contaminants, the preparations of lipid vesicles disclosed in these patents have limited applications.